Most pregnancies last around 40 weeks (or 38 weeks), so typically the The best way to estimate your due date is to count 40 weeks or 280 days, from the first day of your last menstrual period (LMP).
Another The way to do it is to subtract three months from the first day of your last period and add seven days. So if your last period started on April 11, you’d count back three months to January 11 and then add seven days, which means your due date would be January 18.
This is how your doctor will estimate your due date — and it’s a pretty solid target. But remember: It’s just as normal to deliver a week or two before or after.